Locks for sliding doors and windows frequently employ a tongue that is in the form of a “hook”. The tongue pivots about an axis generally normal the plane of the door or window and moves angularly between a retracted position within the lock body and an extended position engaging a striker plate or door jamb. For added security it is known to employ two of these tongues. The mechanism to drive these two tongues between the two positions is complex and therefore costly to manufacture. A further disadvantage in that regard is reliability of the lock. It is also difficult to fit the lock within the space provided on the door.